General Tissues and Epithelial Tissue
Your body contains about 200 different cell types organized into just four broad tissue categories. Each tissue type serves specific functions - epithelial tissue covers surfaces, connective tissue (making up 85% of your body) provides support, nerve tissue conducts electricity, and muscle tissue contracts.
Epithelial tissue forms sheets of tightly packed cells that cover surfaces. The bottom layer attaches to a base while the top remains open to the environment. Simple epithelium has only one layer and is named by cell shape (squamous, cuboidal, or columnar). Stratified epithelium contains multiple layers and is named by the shape of its top cells.
The four main types of epithelia include simple squamous (thin, scaly cells), simple cuboidal (square or round cells found in glands), simple columnar (tall, narrow cells lining digestive and urinary tracts), and stratified epithelia. Stratified epithelia can have 2-20 layers with new cells continually forming at the bottom through mitosis while older cells move upward.
Did you know? Your skin replaces itself completely about every 27 days! This happens through a process where new cells form at the bottom layer while old cells move up and eventually flake off.
